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[on:]

Hi,

I want to control the direction of a DC motor...I was doing it with four SPST relays which I realize is dumb. I got a 12V DPDT relay and was just wondering how to hook it up. There are two coil pins, two NC pins, two "Core" (??) pins and two NO pins.
I saw this tutorial: http://arduino.cc/playground/Main/DCMotorControl and it said the wiring is wrong and I should ask about it....

So do I hook two arduino pins to the two "core" pins, the motor to the coil and the two NC pins to ground/12V and the NO pins to 12V/ground? Then I also use a transistor (like a tip120) with a diode to connect the pins to the arduino, no?

just want to make sure I'm doing it right.
Thanks.

[Reply #1 on:]

I suspect the coil pins should be connected to the 'duino, with a reversed diode to kill the spike
Check that pulls the relay first
You should hear it click on and off

[Reply #2 on:]

Take a look at this link, it shows you how to do that.
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

[Reply #3 on:]

I want to control the direction of a DC motor...I was doing it with four SPST relays which I realize is dumb. I got a 12V DPDT relay and was just wondering how to hook it up.

Using 4 SPST relays isn't necessarily "dumb"; using a DPDT relay may be "dumb" - depending on if you need to be able to turn the motor off. If you do - then a good compromise is two SPDT relays.

The main reason to use SPST relays is the fact that in many cases, you can find larger, higher-current (for the contacts) relays (and for the really large ones, they are called "contactors") easier than you can a DPDT. As long as you make sure that only the proper pair are energized to avoid shoot-thru (and smoke - or fire, depending on what you are controlling) - using four SPST relays/contactors may be what is needed.

Similarly, SPDT relays can be found with higher contact current capability (for a given price) than can an DPDT relay; and if you need an "off" position for the motor, this is a better way to do it than say, using a DPDT relay and a separate SPST relay to control power - mainly because "off" when using SPDT relays is a "brake" function (whereas the DPDT/SPST combo, off is "coast" - now, if you need coasting instead of braking, that may be the better choice).

Also - four SPST relays can give you the choice of coasting or braking for "off" - so there's that, too.